While the present invention can be used in any suitable belt coating process, for the sake of clarity, it will be described in reference to a fuser belt useful in an electrostatic marking system.
Generally, in a commercial electrostatographic marking or reproduction apparatus (such as copiers/duplicators, printers, multifunctional systems, or the like), a latent image charge pattern is formed on a uniformly charged photoconductive or dielectric member. Pigmented marking particles (toner) are attracted to the latent image charge pattern to develop this image on the dielectric member. A receive member, such as paper, is then brought into contact with the dielectric or photoconductive member and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric member to a fusion station, and the image is fixed or fused to the receiver member by heat and/or pressure to form a permanent reproduction thereon. The receiving member passes between a pressure roll and a heated fuser belt, roll, or element.
Sometimes copies made in xerographic or electrostatic marking systems have defects caused by improper fusing of the marking material or the fuser itself. The incomplete fusing can be the result of many factors, such as defects in the toner pressure or fuser belts or rolls. Defects in the fuser belts or rolls can be caused by improper compression set properties or flaws resulting from extended use or more often to improper coating of the fuser substrates during imprecise manufacture. Sometimes these flaws occur because of degrading of the silicone coating during the heat-curing step.
An electrographic fuser roll element includes metallic substrates such as aluminum, an elastomeric cover layer, usually a silicone, and at least one coating over the silicone, generally made of a fluoropolymer, such as Teflon® (a trademark of DuPont). In other cases, the fuser belts contain only a polyimide substrate with a Teflon overcoating. The fuser belt element may or may not contain an elastomer cover layer or silicone. In some cases, the electrographic fuser belt element includes polyimide substrates, an elastomer cover layer usually silicone and an overcoating over the silicone, such as Teflon® or Viton® (Trademarks of DuPont).
This invention and its various embodiments are concerned with the manufacturing process for making these coated fuser elements, including fuser belts, rolls, and other configurations. While for clarity the term “fuser structure or member” will be used throughout this disclosure and claims, any suitable fusing configurations are intended to be included, such as belts, rolls, and other fuser structures.
As above noted, fuser belts used in electrostatographic marking systems generally comprise a polyimide layer coated with one or more elastomer layers, such as silicone. Conventional fuser belt polyimide layers for a belt circumference of 950 mm are 75-85 μm. Such thickness has been desired in order to provide strength and durability as the fuser belt presses against the nip of the adjoining compression or pressure roll. For this approximate 950 mm belt, the silicone layer thickness is in the order of 150-600 μm, and the Viton or Teflon overcoating is generally about 15 μm-35 μm thick. However, as the size of the belt changes, appropriate changes in these thicknesses are naturally made. In most embodiments, the fuser belt is provided an outer non-stick surface or covering of polytetra-fluoroethylene, known as Teflon or Viton, trademarks of E.I. DuPont. This outer coating can be of any suitable thickness, depending on the size of the belt.
The use of a fusing member constructed with a non-stick material as a top layer and a heat resistant base layer has been known in the electrostatographic art. Typical non-stick materials that may be used include polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA), polychlorotrifluoroethylene (ECTFE), ethylene-chlorotrifluoroethylene (ECTFE), ethylene-chlorotrifluoroethylene (ECTFE), ethylene-tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF), and blends of these materials.
Fluoropolymer resin by itself, though an excellent non-stick material, is not compliant. Silicone compounds, on the other hand, are compliant. It is known in the art form a fuser member having a material combining the non-stick properties of fluoropolymer resins and the compliant properties of silicone elastomers.
Currently in the prior art, there are two approaches for making Teflon over silicone fuser members. The first approach is to mold the rubber in between the substrate and the fluoro-plastic sleeve, the other method coats the fluoro-plastic on the silicone and cures it on the silicone. The latter method is preferred because of improved durability and wear. The coating method typically involves the following process: a substrate is primed, silicone rubber is molded, cured and optionally post cured; the required dimension is usually obtained by grinding; the fluoropolymer layers are applied usually by spraying but may also be flow-coated or powder-coated. The whole member is baked above the melting or sintering point (300° C.) of the fluoropolymer, then the cured surface is usually polished. The fluoropolymer coating layers typically comprise an adhesive (often silane) and/or polyimide/polyamide coating, an optional fluoropolymer primer layer, an optional mid coat layer and a topcoat fluoropolymer layer that is in contact with the media and toner.
There are several advantages to the latter approach. The fluoropolymer layer can be made thinner than a sleeve, less than the ˜30 μm thick with a tight distribution. Also, there is more choice in the material that can be applied. This configuration has been shown by machine testing to yield a more durable and therefore a longer lived fuser member than the sleeved approach by better resisting damage from paper; stripper fingers or sensors that contact the member.
A problem with this approach is that silicone is degraded at high temperatures, ˜>260° C. PQ defect. In fact, both of these failure modes have been observed indicating there is not sufficient process latitude or process control.
The temperatures required to bake the fluoropolymer layer in a Teflon over silicone system (TOS) usually damages the properties of the silicone rubber, specifically the compression set properties to the point where set of the member is often seen in the form of flat spots or finger-induced dents. Currently, one may process at a temperature lower than that preferred for Teflon cure to improve set properties at the expense of Teflon properties (primarily wear); the result is degraded life due to occasional poor wear or set. Alternately, the TOS member may be “Molded in Place”, MIP, where silicone rubber is molded in between an extruded Teflon sleeve and substrate. This approach has the disadvantage of a relatively thick fluoropolymer layer with wider dimensional tolerances and less durability.
Present programs are seeking a 12″ belt fuser with a material configuration consisting of a polyimide base with silicone and a Teflon release layer. In order to cure the Teflon, the belt must be heated to temperatures which exceed the material limitations of the silicone. The current lab IR oven which would normally be a viable option to this problem is not large enough to handle the size of this belt. A replacement IR oven is in excess of $200 k with a significant lead time. If using the current belt mandrel, the time to heat up the belt to cure temperatures in a conventional oven would significantly degrade the silicone material properties. There are no known solutions to delivering this belt configuration with the current lab equipment.